1. Field of the Invention
The present invention relates to a thermal-transfer printer, particularly relates to a thermal-transfer printer having a thermal head for thermally transferring ink onto a sheet.
2. Description of the Related Art
Conventionally, there is known a thermal-transfer printer having a thermal head for thermally transferring ink onto a sheet.
In JP-A-2-160558, there is disclosed a thermal-transfer printer for pressing a platen roller to a thermal head by pivoting a positioning member for supporting the platen roller centering on a predetermined axis.
In JP-A-3-049961, there is disclosed a thermal-transfer printer for restraining a thermal head from producing a positional shift in a longitudinal direction by providing an attaching plate with a compression spring for restraining the attaching plate attached with the thermal head from moving in a longitudinal direction of the thermal head.
In JP-A-9-071022, there is disclosed a thermal-transfer printer for restraining a thermal head from moving in a direction along a shaft by bringing a supporting piece into contact with a restricting member even when a force in the direction along the shaft is exerted to the thermal head by providing the restricting members to both sides of the supporting piece for attaching the thermal head to the shaft.
FIG. 9 is a perspective view showing a overall structure of a thermal-transfer printer having a thermal head for thermally transferring ink onto a sheet according to an example of a prior art. Further, FIG. 9 shows a state of removing an ink cartridge of the thermal-transfer printer. FIG. 10 is a top view of the thermal-transfer printer according to the example of the prior art shown in FIG. 9. FIG. 11 and FIG. 12 are sectional views taken along XI—XI line shown in FIG. 10. FIG. 13 is a disassembled perspective view showing a structure of a heating portion of the thermal-transfer printer according to the example of the prior art shown in FIG. 9. FIG. 14 is an enlarged sectional view showing a structure of attaching a head attaching arm of the thermal-transfer printer according to the example of the prior art shown in FIG. 9 to a supporting shaft. First, an explanation will be given of a structure of the thermal-transfer printer having the thermal head according to the example of the prior art.
As shown in FIG. 9, a main body frame 101 is provided in the thermal-transfer printer having the thermal head according to the example of the prior art. A first conveying roller 102 for conveying a sheet 200 (refer to FIG. 10) is provided on this side of a front side of the main body frame 101. A holding roller 103 for restraining the sheet 200 from floating up from the first conveying roller 102 is provided on an upper side of the first conveying roller 102. Further, a second conveying roller 104 for conveying the sheet 200 is provided on a rear side of the first conveying roller 102. A holding roller 105 for restraining the sheet 200 from floating up from the second conveying roller 104 is provided on an upper side of the second conveying roller 104.
A platen roller 106 for conveying the sheet 200 is provided on a rear side of the second conveying roller 104. Further, an ink cartridge 107 is attached to a central portion of the main body frame 101 as shown in FIG. 10 through FIG. 12. As shown in FIG. 11, an ink sheet 107a adhered with ink for transferring onto the sheet 200 is contained in the ink cartridge 107. The ink of the ink sheet 107a is constituted by three colors of inks of C (cyan), M (magenta) Y (yellow).
Further, as shown in FIG. 9 and FIG. 11, a heating portion 108 for thermally transferring the ink of the ink sheet 107a onto the sheet 200 is provided on a depth side of the central portion of the main body frame 101. The heating portion 108 is pivotally supported by a pair of supporting shafts 109. Further, the heating portion 108 is urged in a direction of pivoting upwardly by a torsion coil spring 110 mounted to one of the supporting shafts 109. Further, as shown in FIG. 13, the heating portion 108 is constituted by a thermal head 111, a pair of head attaching arms 112, a pair of bearing members 123, a pair of head supporting arms 113, a compression coil spring 114 and a heat radiating plate 115. The thermal head 111 is provided for thermally transferring the ink of the ink sheet 107a onto the sheet 200 by heating the ink sheet 107a contained in the ink cartridge 107 (refer to FIG. 11). Further, as shown in FIG. 13, a pair of spring attaching boss portions 111a is provided at an upper portion of the thermal head 111.
The pair of head attaching arms 112 include head attaching portions 112a attached with the thermal head 111 and supporting shaft attaching portions 112b for supporting the supporting shafts 109. As shown in FIG. 10, the head attaching arm 112 is formed to extend in a direction along a direction of conveying the sheet 200. Further, as shown in FIG. 13, the head attaching portions 112a of the head attaching arms 112 are attached with the thermal head 111. Further, a fitting hole 112c is provided at the supporting shaft attaching portion 112b of the head attaching arm 112. As shown in FIG. 14, a bearing member 123 is attached to the fitting hole 112c of the head attaching arm 112. The supporting shaft 109 is inserted into the bearing member 123.
Further, as shown in FIG. 13, the pair of head supporting arms 113 are attached to side faces on outer sides of the head attaching arms 112. A spring pressing portion 113a is formed at an upper portion of the head supporting arm 113. Further, a boss portion 113b is provided at a side face of one end portion of the head supporting arm 113. Further, a fitting hole 113c is provided at other end portion of the head supporting arm 113 at the position in correspondence with the fitting hole 112c of the head attaching arm 112. The supporting shaft 109 is inserted into the fitting hole 113c of the head supporting arm 113. Thereby, the head supporting arm 113 is pivotally supported by the supporting shaft 109 along with the head attaching arm 112.
Further, the compression coil spring 114 is mounted to the spring attaching boss portion 111a of the thermal head 111. An upper portion of the compression coil spring 114 is pressed by the spring pressing portion 113a of the head supporting arm 113. The compression coil spring 114 is provided for pressing the thermal head 111 to a side of the platen roller 106 (refer to FIG. 9) by a predetermined pressing force. Further, as shown in FIG. 13, the heat radiating plate 115 is attached to an upper portion of the thermal head 111. The heat radiating plate 115 is provided for radiating heat of the thermal head 111.
Further, a pressing member 116 is provided to be brought into contact with the respective boss portions 113b of the pair of head supporting arms 113. The pressing member 116 is constituted by a pair of pressing arms 117 brought into contact with the boss portions 113b of the head supporting arms 113, and a connecting member 118 for connecting the pair of pressing arms 117. Further, the pressing member 116 is constituted to pivot by constituting an axis thereof by the connecting member 118. Further, the pressing member 116 is provided to pivot the heating portion 108 in the direction of bringing the thermal head 111 into contact with the ink sheet 107a (refer to FIG. 11) by pressing down the boss portion 113b of the head supporting arm 113. Further, as shown in FIG. 13, a gear engaging portion 117a is formed at one of the pair of pressing arms 117. A drive gear 119 is brought in mesh with the gear engaging portion 117a of the pressing arm 117. As shown in FIG. 10, a middle gear 120 is brought in mesh with the drive gear 119 and a drive transmitting gear 121 is brought in mesh with the middle gear 120. A motor side drive gear 122a of a motor 122 attached to a side face of the main body frame 101 is brought in mesh with the drive transmitting gear 121.
Next, an explanation will be given of operation of the thermal-transfer printer having the thermal head according to the example of the prior art in reference to FIG. 10 through FIG. 12 and FIG. 14. As the operation of the thermal-transfer printer having the thermal head according to the example of the prior art, as shown in FIG. 11, the sheet 200 is conveyed in an arrow mark D direction in FIG. 11 by rotating the first conveying roller 102 in an arrow mark C direction in FIG. 11. The sheet 200 is conveyed further in the arrow mark D direction in FIG. 11 by rotating the second conveying roller 104 in the arrow mark C direction in FIG. 11. The sheet 200 conveyed by the second conveying roller 104 reaches the platen roller 106.
At this occasion, rotation of the motor side drive gear 122a rotated by driving the motor 122 (refer to FIG. 10) is transmitted to the gear engaging portion 117a of the pressing arm 117 via the middle gear and the drive gear 119. Thereby, the pressing arm 117 is pivoted in an arrow mark E direction in FIG. 11. When the pressing arm 117 is pivoted in the arrow mark E direction in FIG. 11, the boss portion 113b of the head supporting arm 113 is pressed down by the pressing arm 117. Thereby, the heating portion 108 disposed at an escaping position as shown in FIG. 11 is pivoted in an arrow mark F direction by constituting an axis thereof by the supporting shaft 109. When the heating portion 108 is pivoted in the arrow mark F direction in FIG. 11, as shown in FIG. 12, the thermal head 111 of the heating portion 108 is brought into contact with the ink sheet 107a of the ink cartridge 107, and the ink sheet 107 and the sheet 200 are pressed to the platen roller 106. Thereby, the ink sheet 107a is heated by the thermal head 111 and therefore, ink of one color in three colors of inks of C (cyan), M (magenta) and Y (yellow) of the ink sheet 107a is thermally transcribed onto the sheet 200. At this occasion, the thermal head 111 is exerted with a force in a direction along a direction of conveying the sheet 200 from the rotating platen roller 106 (arrow mark D direction in FIG. 12).
Further, the sheet 200 is further conveyed in the arrow mark D direction in FIG. 12 and the ink of the ink sheet 107a is thermally transcribed up to a rear end of the sheet 200 by the thermal head 111. When the ink is thermally transcribed up to the rear end of the sheet 200, the sheet 200 is conveyed in an arrow mark H direction in FIG. 12 by rotating the platen roller 106, the second conveying roller 104 and the first conveying roller 102 in an arrow mark G direction in FIG. 12. At this occasion, rotation of the motor side drive gear 122a rotated by driving the motor 122 (refer to FIG. 10) is transmitted to the gear engaging portion 117a of the pressing arm 117 via the drive transmitting gear 121, the middle gear 120 and the drive gear 119. Thereby, the pressing arm 117 is pivoted in an arrow mark I direction in FIG. 12. In accordance with pivoting the pressing arm 117 in the arrow mark I direction in FIG. 12, the heating portion 108 urged in an upper direction by the torsion coil spring 110 (refer to FIG. 10) is pivoted in an arrow mark J direction in FIG. 12 by constituting an axis thereof by the supporting shaft 109. Thereby, as shown in FIG. 11, the heating portion 108 is moved to the escaping position. Further, the sheet 200 is conveyed in the arrow mark H direction in FIG. 11 up to a vicinity of the first conveying roller 102.
Further, thereafter, by repeating operation similar to the above-described operation twice, remaining two colors of inks of C (cyan), M (magenta) and Y (yellow) are transcribed onto the sheet 200. Thereby, an image is printed on the sheet 200.
In the thermal-transfer printer having the thermal head according to the example of the prior art shown in FIG. 9, dimensions of fitting the supporting shaft 109 and the bearing member 123 are designed such that the heating portion 108 can be pivoted relative to the supporting shaft 109. However, owing to a dimensional error, as shown in FIG. 14, there is brought about a drawback that there is frequently a case of producing a clearance 124 between the bearing member 123 and the supporting shaft 109. Thereby, rattling is brought about between the bearing member 123 and the supporting shaft 109 and therefore, there is brought about a drawback that rattling is caused in the head attaching arm 112 attached with the bearing member 123 relative to the supporting shaft 109. Therefore, rattling is caused in the thermal head 111 attached to the head attaching arm 112 in the direction of conveying the sheet 200 and therefore, there is brought about a drawback that a printing position of the thermal head 111 relative to the sheet 200 is shifted in the direction of conveying the sheet 200. As a result, there occurs a problem that nonuniformity in printing is brought about.
Further, according to the thermal-transfer printer disclosed in JP-A-2-160558, mentioned above, a structure for restraining rattling of the platen roller for pressing a sheet to the thermal head is not disclosed and therefore, there is brought about a drawback of causing rattling in the platen roller in the direction of conveying the sheet. Thereby, also in the thermal-transfer printer disclosed in JP-A-2-160558, mentioned above, similar to the thermal-transfer printer owing to the embodiment of the prior art shown in FIG. 9, there occurs a problem that nonuniformity in printing is brought about owing to the fact that a printing position of the thermal head relative to the sheet is shifted in the direction of conveying the sheet.
Further, according to the thermal-transfer printers disclosed in JP-A-3-049961 and JP-A-9-071022, mentioned above, whereas the structure of restraining a positional shift of the thermal head in a longitudinal direction or the direction along the shaft (direction orthogonal to the direction of conveying the sheet) is disclosed, there is not disclosed a structure for restraining rattling of the thermal head from being brought about in the direction of conveying the sheet. Therefore, also in the thermal-transfer printers disclosed in JP-A-3-049961 and JP-A-9-071022, mentioned above, similar to the thermal-transfer printer according to the example of the prior art shown in FIG. 9, there poses the problem that nonuniformity in printing is brought about owing to the fact that the printing position of the thermal head relative to the sheet is shifted in the direction of conveying the sheet.